1. Field of the Invention
The present invention relates to the art of cellulosic substrate coatings. Specifically, the coating of the invention is particularly selected to provide grease, oil and wax resistance to paper substrates without the deleterious inclusion of fluorocarbons, while maintaining other desired properties.
2. Discussion of the Prior Art
Water based mineral coatings for paper substrates can consist of virgin or recycled fiber, or blends of both for substrates for all types of paper packaging applications or markets. The use of minerals suspended in water for application onto paper, paperboard, bagstock, ticket stock, or linerboard, bleached or natural kraft is well known in the art. Generally, the known paper coatings include a clay (or other filler to impart color), a polymeric binder, and a fluorocarbon or wax to provide the desired grease resistance.
These coatings have been particularly developed to additionally provide industry desired brightness. Specifically, industry requires minimum GE brightness (approximately 50) to a maximum GE brightness (approximately 90). GE brightness is defined by Technical Association of the Pulp and Paper Industry (TAPPI) as a directional brightness measurement wherein the surface to be tested is illuminated with essentially parallel light beams at a 45° angle, and is described in TAPPI T 452 “Brightness of Pulp, Paper, and Paperboard (Directional Reflectance at 457 nm).”
Additionally, the selected coating must withstand the stresses which often occur during processing of the coated paper. In particular, flexibility of the coating for forming containers and packages without flaking or fracturing is required. Smoothness is necessary for high quality graphics printing, as well as a high degree of bonding to the paper surface, as measured by the wax-pick test method, is necessary. Moreover, the ability to resist the converting rigors of heat, abrasion, and pressure while passing through equipment for die cutting, scoring, printing, gluing, strapping, resisting like environments for the corrugating converting process, glueability with hot melt adhesives or cold set adhesives, and excellent fiber tear test results must be provided.
U.S. Pat. No. 5,674,961 to Fitzgerald, discloses a typical oil, water and solvent resistant paper. Specifically, a fluorocarbon is impregnated into a paper, cardboard, paperboard or cardboard substrate to impart resistance. Additionally, a synthetic base is rendered resistant by impregnating with a fluoronated component, as described in U.S. Pat. No. 5,330,622 to Honnotat et al. The inclusion of such fluorocarbons is recognized across the industry as a useful and economic method to add oil, water and solvent resistivity to paper and other fibrous products.
However, it has recently been recognized by the U.S. Environmental Protection Agency (EPA), as well as the Canadian Department of Health and Welfare, and the German BGVV, that such fluorocarbons may have deleterious health consequences. As reported by the EPA, certain fluorocarbons (e.g. perflourooctanesulfonic acid, its derivates and salts) have been found in the systems of humans and other animals, resulting in raised concerns regarding potential developmental, reproductive and systemic toxicity. It has been proposed by the EPA that the manufacture and/or release of such chemicals cease to limit build-up in both animal populations and the environment to avert adverse consequences therein.
The desire to generate a superior grease, oil, and wax resistance mineral white coatings for food and machinery packing has been a focal point of marketing display packages that remain attractive graphically by resisting stains from external and internal sources. Being economically formulated is also an industry requirement. Complying with regulations of the EPA, Canadian Health and Welfare, German BGVV, and addressing all domestic and international compliances to permit distribution internationally is without issue. The coating should also be repulpable at mills throughout the world. The presence of wax or wax containing coatings presents a problem in repulping recycled paperboard or box materials.
Therefore, there exists a need in the art to provide a coating which gives resistance to grease, oil and wax which is also environmentally palpable. Essentially, this requires the development of a coating which is free of fluorocarbons and other volatile organic component (VOC) emissions, while maintaining a degree of repulpability and the ability to be applied during the manufacture of the paper itself or during an off-line coating process.